首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   224篇
  免费   21篇
林业   12篇
农学   3篇
基础科学   3篇
  20篇
综合类   37篇
农作物   5篇
水产渔业   19篇
畜牧兽医   129篇
园艺   8篇
植物保护   9篇
  2020年   3篇
  2019年   7篇
  2018年   5篇
  2017年   5篇
  2016年   4篇
  2015年   3篇
  2014年   6篇
  2013年   24篇
  2012年   5篇
  2011年   9篇
  2010年   9篇
  2009年   4篇
  2008年   11篇
  2007年   8篇
  2006年   5篇
  2005年   7篇
  2004年   9篇
  2003年   10篇
  2002年   7篇
  2001年   7篇
  1999年   6篇
  1998年   4篇
  1997年   3篇
  1996年   3篇
  1992年   3篇
  1991年   5篇
  1990年   6篇
  1989年   3篇
  1988年   2篇
  1986年   5篇
  1985年   6篇
  1983年   4篇
  1979年   5篇
  1978年   6篇
  1976年   4篇
  1975年   4篇
  1974年   1篇
  1971年   1篇
  1970年   1篇
  1969年   2篇
  1967年   4篇
  1966年   1篇
  1964年   1篇
  1952年   2篇
  1939年   1篇
  1934年   1篇
  1917年   1篇
  1916年   1篇
  1915年   1篇
  1912年   1篇
排序方式: 共有245条查询结果,搜索用时 0 毫秒
241.
Bartonella henselae is occasionally associated with neurological dysfunction in people and some experimentally infected cats. The purpose of this study was to determine whether B henselae seroprevalence or titer magnitude varies among cats with neurological disease, cats with non-neurological diseases, and healthy cats while controlling for age and flea exposure. There was no difference in B henselae seroprevalence rates between cats with seizures and cats with other neurological diseases. Cats with non-neurological disease and healthy cats were more likely than cats with neurological disease to be seropositive. While the median B henselae antibody titer was greater in cats with seizures than in cats with other neurological disease, the median B henselae antibody titer was also greater in healthy cats than cats with seizures. The results suggest that titer magnitude cannot be used alone to document clinical disease associated with B henselae infection and that presence of B henselae antibodies in serum of cats with neurological disease does not prove the clinical signs are related to B henselae.  相似文献   
242.
243.
The economics of enforcement is traditionally modelled using rational agents assumed to act according to their expected economic utility. In this investigation we derive this expectation by implementing a stochastic simulation model to integrate across associated levels of uncertainty using Monte Carlo. The model is developed for the South Georgia toothfish longline fishery, in which legal catches are strictly managed according to the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) conservation measures. Assuming full compliance in the legal fishery, this investigation deals with the role of a fishing patrol vessel (FPV) in excluding illegal fishing vessels. Both legal and illegal fleets are dynamic. For the legal fleet, catch is set by a harvest control rule within the model framework, with vessels leaving if fishing becomes unprofitable. The illegal catch is determined by the number of vessels operating, which predicts catch on the basis of an estimated production function. The exit of illegal vessels is determined by the probability of detection by the FPV, which is a function of days spent on patrol, and estimated profits. The entry of illegal vessels occurs at a fixed mean rate, with the model integrating over uncertainty in this parameter. An obvious trade off exists in that higher levels of illegal activity lead to lower expected returns to the legal fleet. We thus provide a cost-benefit framework for investigating the trade-offs associated with decisions on enforcement in the fishery, and confirm that current enforcement effort levels are well justified.  相似文献   
244.
Rainbow trout with initial body weight 1144 g were fed two diets with high (feed A) or low (feed B) water stability for 6 weeks. During the last 2 weeks either stable or fluctuating oxygen saturation, salinity and temperature was introduced. High water stability of the feed was associated with harder pellets, less dust formation and less broken pellets compared to feed with low water stability. During the first 4 weeks, feed intake was 23% higher in trout fed diet B than in those fed diet A. Fluctuating environment resulted in a severe drop in feed intake for both dietary groups. At termination of the trial, stomachs of trout fed feed B contained mashed pellets and free water and oil. Stomachs of trout fed feed A contained more intact pellets and little fluid. The apparent digestibility of protein, starch, dry matter and energy was highest in feed A. The apparent digestibility of P and Zn was highest at stable environment, and the absorption of P was highest from feed A. In conclusion, physical quality affected the nutritional value of the feeds, and differences in nutritional value at stable or fluctuating environment appeared to be related to feed intake.  相似文献   
245.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号